This invention relates to the assembly of a turbomachine rotor, comprising in particular two bladed-discs separated by a spacer used for cooling or sealing.
A classical construction of rotors comprises successive discs equipped with flanges that are in contact with each other and connected using a bolting system. There are circular spacers around the flanges. Cooling air for the discs can flow inside these spacers and their outer surfaces may carry arrangements to ensure a seal with the fixed blades of the stator. The U.S. Pat. No. 4,730,982-A is such an example. The spacers are normally bolted to the flanges, but this design is not feasible if the discs are designed to be fabricated from a single blank, or welded, which dispenses with the flanges.
The invention relates to a new assembly arrangement of rotors comprising two consecutive discs and an intermediate spacer, that is adapted to the permanently connected discs where the bolted flanges have been dispensed with, which requires the design of a different system for the attachment of the spacer.
One solution has already been suggested in the document U.S. Pat. No. 4,277,225-A. The spacers are equipped with pins mounting with the cross section being similar to that of the blade roots and which slot into the serrations of the blade roots. Axial locking of several stages of blades is achieved by compressing the stack of spacers and blades, with the pins mounting of the spacers butting up against the ends of the blade roots.
This design is not described here. It is not clear that the compression of a complex stack would be satisfactory in the presence of vibrations, and very precise manufacturing of the components is necessary in order to achieve a correct assembly, especially such that the pins mounting of the spacers are accurately adjusted with the discs located at either end. These pins mounting have a very complicated cross section. It is also necessary for the discs to be the same, and that the rotor is thus cylindrical. Finally, the inventor has ignored the continuity of the spacers in an angular direction, each one having only one pin mounting on each side. The neighbouring spacers are in contact through the inner lands of the ribs which cover the front of the discs, in which have to be formed additional serrations just to allow the ribs to pass.
In the most general definition of the invention, the spacer comprises a cover surrounding one of the discs (in which are formed location serrations for the blade roots), tongues that can slide into the serrations, the inner radial thrust faces on the matching faces formed in one of the discs, and the outer axial thrust faces, the inner radial thrust faces being located on the tongues. Furthermore the invention is original in that the outer axial thrust faces comprise the primary faces that press against one of the discs, and the secondary faces opposite the primary faces, that press on a seal associated with the other discs.
Later on it will be shown how this spacer meets the requirements of a rigid assembly despite the absence of bolting and without compromising the sealing functions, and even improving the potential for disc cooling. Another essential benefit that is achieved is the simplification of assembly, together with a weight reduction and possibly better strength, due to the connection of the discs, the disposal of bolts and an improved trueness of the shape of the separate units.
It is to be noted that the tongues, though analogous to the ribs that join the spacers as sections of a circle in the document U.S. Pat. No. 4,277,225-A, have other functions and are not located in the same way, since above all they are used to take the radial thrust of the spacer on the disc. They must be capable of sliding in the serrations of the discs, but in reality they are not located there when the build is completed. In the absence of a method equivalent to the pins mounting, that take the thrust loads in the disc serrations to locate the spacers, the latter are located entirely between the discs. They are continuous around a circle, which allows them to be held in place by a single collar located on the side of one of the discs.
In a beneficial embodiment, the previous design is improved whereby the tongues and the cover form the boundary for the cooling passages of the discs, the passages also extending into the serrations and under the roots of the blades, and such that the tongues extend between the serrations, the first outer axial thrust faces being on the tongues, and the complementary faces being located on a crown formed on the side of the first disc. Thus, the cover, the tongues and the serrations combine to unexpectedly achieve the same function, all different from those described earlier i.e. that of rotor cooling, by exploiting the fact that the spacer is rotated after having been inserted between two discs so that the tongues are no longer opposite the serrations but between them and thus splitting the air flow across the serrations.
Being less mechanically stressed than the normal spacers since it serves no purpose in the assembly of other components against which it would be compressed, and the fact that the only connection to the discs is through a circular loading on a collar and an axial thrust against a seal, the spacer may be made of light construction, and even made from composite materials if the cooling is adequate.